Just a note to those that think A.O. Smith doesn't want to sell you a tankless water heater. That is false, what they want you to do is make an informed choice when you are considering a tankless unit. They want people to realize here in the USA we take the amount of water we use at once for granted, and if you install a single unit in a high demand situation the water will not get hot enough to be satisfactory. Which is why they point out it could be costly to replace your tanked heater with a tankless unit.

For some homes two units are needed to provide you enough hot water for those peak usage times. Below is a pic showing how two units are installed. Just a note if you are just washing your hands only one unit fires up, the only time the second unit will turn on is when you exceed the flow rate of the first unit to get the desired temperature.

Another note about the cost of installing tankless units is gas pipe sizing. Most Tank units only use 1/2" piping due to BTU ratings which the most common is 40,000 BTU's. Tankless units on low flow mode usually draws 25,000 BTU's and full flow mode can go as high as 199,000 BTU's, some units can go higher but they must follow boiler installation codes once they go over 200,000 BTU's. Well in most cases you will need to tap off the main gas supply coming into the home with a 3/4" line to the tankless unit, if you have to install multiple units as this next picture you will see they ran 1 1/4" pipe up to the units then reduced it down to the 3/4" to the units, This insures that when all three units fire up at their 199,000 BTU's they will get enough gas to run at that setting. So this is the other part of the expense that A.O. Smith is talking about.

Ah yes, my local plumbing supply hands that out to homeowners that come in asking about tankless heaters. I am going to make jpgs of them 4 pages and post them here in this thread too. I like to see this thread stay on the facts of tankless heaters instead of a battle ground like the other threads ended up becoming. Thank you Redwood for posting this PDF